Signal repeating systems like distributed antenna systems (DAS) are commonly used to extend wireless coverage into buildings, between buildings, in tunnels, and into various other areas, where RF signal penetration from base stations is limited. Antenna units and antennas are distributed through a building and are optimally placed to provide ubiquitous coverage inside the building or other areas.
Digital distributed antenna systems often consist of one or more master units (MU) that are connected to various base transceiver stations (BTS) of various cellular providers employing different air interfaces. A series of physically separated remote antenna units (RAUs) are each connected to an MU via a digital serial link. The MU down converts and digitizes (ADC) the Downlink (DL) signals from the base station(s) and time division multiplexes (TDM) the digital data into frames that are then transmitted over appropriate serial data links to the RAUs. The RAUs digital-to-analog convert (DAC) the digital data and up convert the respective analog signals to the required RF format for transmission to fixed or mobile subscribers in the system. In a similar manner, the RAUs down-convert and digitize Uplink (UL) signals from the fixed/mobile users and transmit the digitized data back to the MU. The MU digital-to-analog may convert the signals from the mobile/fixed subscribers and up-convert them to the appropriate RF format for transmission to the various BTSs or the MU may forward the digital data directly.
While such digital DAS systems provide desirable coverage into buildings and sheltered areas, the digital serial link between the MU and RAUs can present a traffic bottleneck for a Digital DAS system. The data rate on the digital serial link is often limited to around 10 Gbps due to the cost and the physical media that is used (e.g. optical fiber or twisted pair cable) for the serial link. To overcome this limitation, one solution is to implement multiple digital serial links arranged in parallel to transmit the digitized RF data between the MU and RAUs. However, as may be appreciated, using multiple digital serial links is expensive and can significantly increase installation costs for wideband systems. Furthermore, the ability to upgrade or add additional parallel serial links to existing legacy DAS installations may not be available, or may be prohibitively expensive.
Another factor that further presents an issue with respect to signal traffic is the implementation of Multiple-Input Multiple-Output (MIMO) systems utilizing multiple signal streams for improved communications. Such MIMO systems incorporate multiple signals from the base stations, as well as multiple antennas, such as at the RAUs that are utilized within a MIMO system. Those multiple and individual MIMO signals must be handled over the serial link of a digital DAS System, thus, increasing the overall traffic that must be handled.
Accordingly, it is desirable to improve communication signal traffic flow in a digital DAS system, and particularly to address system bottlenecks associated with a digital serial link. Furthermore, it is desirable to enhance signal traffic within a digital DAS system that is implemented for handling MIMO signals.